The invention has as its object a method for detecting the presence and the relative position of a diffuse reflecting coating, such as a film of moisture, on the surface of a translucent medium and a device for implementing the method.
Used, e.g., in vehicle windshields, such a method can be seen as the central function of a system for determining the degree of visibility.
The methods known until now for this purpose are based primarily on sensors that detect a film of moisture on a surface by means of a capacitive or resistive operating principle and that must be thermally coupled to said surface in order to achieve the same coating behavior as the surface being monitored.
Thus, e.g., a circuit arrangement for measuring moisture on the windshield of a vehicle is disclosed in DE 44 28 111 A1, in which the resistance between electrodes on the windshield which are in thermal contact with it is measured.
Detection of other coatings than those caused by moisture and detection of coatings on the surface opposite the sensor cannot be realized with methods of this previously known type.
In addition, a device and a method for detecting the presence and the relative position of coatings on a translucent pane are known from U.S. Pat. No. 4,867,561. Here, an optical sensor array with light from various light sources is applied, wherein these lights sources are arranged in two rows in order to be able to focus light reflected at various boundary surfaces of the pane uniformly on the sensor array. The presence of coatings is evaluated by means of the intensity of the light reflections caused by the various light sources, wherein, in order to normalize the absolute intensities, a region of sensor arrays is included that are not assigned to any light source.
Because of the number of light sources used in this method, both the device and the method are very expensive. Thus, the light sources involve a significant component cost, not only because of the number of light sources, but also because light sources must be chosen that generate approximately equal light intensities under equal power in order for the method based on intensity values to be implemented. Otherwise, the method must provide for a balancing of light sources of unequal intensity by individual adjustment of power to the light sources.
Starting from the state of the art, the present invention is based on the problem of providing a device and method with which, despite its lower cost, is able to detect and localize any diffuse reflecting coating without contact and thus avoid the problems discussed above.
According to the invention, the problem concerning the method is solved by a process for the detection and localization of diffuse reflecting coatings on a translucent pane through the use of an optical sensor array that contains a receiving unit.